1. Field of the Invention
The present invention is concerned with electrical connectors for securing a connection between two or more electrical wire ends, and more particularly to an improved type of connector known as a twist-on or wire-nut connector having a plastic insulating cap or shell containing a wire coil or spring which is adapted to be screwed down on the stripped ends of the wires to be connected.
2. Description of the Prior Art
Wire-nut connectors (also referred to as twist-on or spring connectors) are well known in the art and have been highly effective in providing a simple device for connecting a plurality of electrical wires together, both mechanically and electrically, and have gained a high degree of commercial acceptance. As a result, a wide variety of such devices have been developed in an effort to simplify their design and manufacture, while increasing their effectiveness. Such devices typically include a plastic insulating cap and a helically coiled spring member contained in the cap. The cap acts as an insulating housing around a tapered, helically coiled spring member and provides an conveniently shaped body for gripping the connector. In this manner, the cap can be twisted onto the plurality of wires with installation torque transmitted from the housing to the spring member thereby forming a connection which is both mechanically secure and electrically conductive.
The prior art connectors suffer several disadvantages, which are properly addressed by this invention.
First, the standard wire-nut connector may be subject to mechanical vibration or changing mechanical load, which will tend to work the wires contained within loose. If the wire nut carries any weight or other load, it will tend to hang on one of the wires. Any relative motion between the individual wires will loosen the wire and compromise the electrical connection. In the worst case, one wire may pop out of the connector, forming a safety hazard, while at the same time, creating a situation in which the remaining wires will more easily come loose.
Second, most wire-nuts are completely open to infiltration by moisture or debris. This can cause several problems including oxidation of the conductors which raises the resistance of the connection and produces excess heat while conducting electricity. Infiltration can also cause deterioration of the wire insulation, electrolysis, and moisture actually forming a conduction path to outside the connector.
Third, if any portion of the conductor is exposed outside the relatively short open end of a standard wire-nut, shock hazard will exist. The ends of the wires must be stripped before insertion in a wire-nut. If too much insulation is stripped or if the insulation prevents any of the wires from entering the wire-nut, then some portion of one of the conductors may be exposed. If any one conductor is exposed, the voltage potential from all the wires will be exposed and will form an electric shock hazard.
According to the present invention, a twist-on connector with a hollow, rigid, insulative cap that is enclosed on an upper or distal end, and open on a proximal end and includes a heat-shrinkable skirt on the open or proximal end will offer a significant improvement over all three of the above disadvantages. Following prior art practices, the hollow, rigid, insulative upper body will be most economically produced through a standard injection molding process as with U.S. Pat. No. 4,924,035 issued to Miller on May 8, 1990. A coil spring, having an outer radial dimension substantially equal to the inner radial dimension of the hollow, rigid, insulative upper body, will be inserted and locked into place in the rigid upper body after its removal from the mold. A heat-shrinkable skirt will be affixed at a predetermined location at the proximal end of the upper body by a chemical and/or mechanical attachment method. The resulting connector of the preferred embodiment will have the appearance of the Dual Durometer Twist-on Connector of U.S. Pat. No. 5,132,494 issued to Burton on Jul. 21, 1992. In contrast to the device described in Pat. No. 5,132,494, however, the lower, flexible portion of the present invention, when treated with a standard heat-gun, will shrink down around the enclosed wires forming a more secure mechanical and electrical connection. The embodiments of the present invention contemplate various processes used to bond the skirt to the rigid body.